Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Physics & Chemistry





On Fri, 22 Nov 1996, Leigh Palmer wrote:

Further, it can be shown that oxidation of iron takes place preferentially at
sites where the iron has been stressed. This can be as simple as a bend in an
iron nail.

Isn't that confounded by crazing of the surface? I don't think I would be
at all convinced that stress alone accounts for the difference, but I
don't know what the actual process is. Still, it seems to me that fresh
surface is exposed when one bends a nail, surface that is not protected
by as much oxide as has formed on the rest of the nail. Perhaps you could
demonstrate it on a seasoned bent nail?

Leigh

Don't charges concentrate on the region of maximum curvature? I think
it's one of Faraday's laws. As the redox takes place, the mobile charge
in the conductor tends to concentrate at the region of greatest bend and
effectively increases the concentration of the reactant at that point.
This increase results in an increase in rate of oxidation leaving the
rest of the nail to be reduced.

At least that's the way I had it explained to me by the chem teacher
here. There is a good photo of this experiment and I think a fair
explanation in Zumdahl's 'Chemistry' 2nd ed. ?

Pete